1. Field of the Invention
The present invention relates generally to very low-power actuation devices and more particularly to very low-power actuation devices for guided gun-fired munitions and mortars that can be scaled to any caliber munitions, including medium and small caliber munitions.
2. Prior Art
Since the introduction of 155 mm guided artillery projectiles in the 1980's, numerous methods and devices have been developed for actuation of control surfaces for guidance and control of subsonic and supersonic gun launched projectiles. The majority of these devices have been developed based on missile and aircraft technologies, which are in many cases difficult or impractical to implement on gun-fired projectiles and mortars. This is particularly true in the case of actuation devices, where electric motors of various types, including various electric motor designs with or without gearing, voice coil motors or solenoid type actuation devices, have dominated the guidance and control of most guided weaponry.
Unlike missiles, all gun-fired and mortar projectiles are provided with initial kinetic energy through the pressurized gasses inside the barrel and are provided with flight stability through spinning and/or fins. As a result, they do not require in-flight control action for stability and if not provided with trajectory altering control actions, such as those provided with control surfaces or thrusters, they would simply follow a ballistic trajectory. This is still true if other means such as electromagnetic forces are used to accelerate the projectile during the launch or if the projectile is equipped with range extending rockets. As a result, unlike missiles, control inputs for guidance and control is required only later during the flight as the projectile approaches the target.
In recent years, alternative methods of actuation for flight trajectory correction have been explored, some using smart (active) materials such as piezoelectric ceramics, active polymers, electrostrictive materials, magnetostrictive materials or shape memory alloys, and others using various devices developed based on micro-electro-mechanical (MEMS) and fluidics technologies. In general, the available smart (active) materials such as piezoelectric ceramics, electrostrictive materials and magnetostrictive materials (including various inch-worm designs and ultrasound type motors) need to increase their strain capability by at least an order of magnitude to become potential candidates for actuator applications for guidance and control, particularly for gun-fired munitions and mortars. In addition, even if the strain rate problems of currently available active materials are solved, their application to gun-fired projectiles and mortars will be very limited due to their very high electrical energy requirements and the volume of the required electrical and electronics gear. Shape memory alloys have good strain characteristics but their dynamic response characteristics (bandwidth) and constitutive behaviour need significant improvement before becoming a viable candidate for actuation devices in general and for munitions in particular.
The currently available actuation devices based on electrical motors of various types, including electrical motors, voice coil motors and solenoids, with or without different gearing or other mechanical mechanisms that are used to amplify motion or force (torque), and the aforementioned recently developed methods and devices (based on active materials, such as piezoelectric elements, including various inch-worm type and ultrasound type motors), or those known to be under development for guidance and control of airborne vehicles, such as missiles, have not been shown to be suitable for gun-fired projectiles and mortars. This has generally been the case since almost all available actuation devices that are being used or are considered for use for the actuation of control surfaces suffer from one or more of the following major shortcomings for application in gun-fired projectiles and mortars:    1. High power requirement for electrical motors and solenoids of different types (irrespective of the mechanical mechanisms that are used to transmit force/torque to the control surfaces), as well as for actuators based on active materials, such as piezoelectric materials and electrostrictive materials and magnetostrictive materials (including various inch-worm designs and ultrasound type motors) and shape memory based actuator designs.    2. Limited dynamic response, i.e., limited peak force or torque and limited actuation speed at full load (equivalent to “bandwidth” in linear control systems), considering the dynamics characteristics of gun-fired projectiles and mortars.    3. Electrical motors of different types and solenoid type actuation devices occupy large volumes in munitions. The volume requirement also makes such electrical actuation devices impractical for medium to small caliber munitions applications.    4. Survivability problems of many of the existing actuation devices at very high setback accelerations of over 50 KG.    5. Reliability of operation post firing, particularly at very high setback accelerations of over 50 KG.    6. The high cost of the existing technologies, which results in very high-cost rounds, thereby making them impractical for large-scale fielding.    7. Relative technical complexity of their implementation in gun-fired projectiles and mortars for control surface actuation.
A need therefore exists for the development of innovative, low-cost technologies that address the aforementioned limitations of currently available control surface actuation devices in a manner that leaves sufficient volume inside munitions for sensors, guidance and control, and communications electronics and fusing, as well as the explosive payload to satisfy the lethality requirements of the munitions.
Such control surface actuation devices must consider the relatively short flight duration for most gun-fired projectiles and mortar rounds, which leaves a very short period of time within which trajectory correction/modification has to be executed. This means that such actuation devices must provide relatively large forces/torques and have very high dynamic response characteristics (“bandwidth”).
The control surface actuation device applications may be divided into two relatively distinct categories. Firstly, control surface actuation devices for munitions with relatively long flight time and in which the guidance and control action is required over relatively longer time periods. These include munitions in which trajectory correction/modification maneuvers are performed during a considerable amount of flight time as well as within a relatively short distance from the target, i.e., for terminal guidance. In many such applications, a more or less continuous control surface actuation may be required. Secondly, control surface actuation devices for munitions in which the guidance and control action is required only within a relatively short distance to the target, i.e., only for terminal guidance purposes.
Such actuation devices must also consider problems related to hardening of their various components for survivability at high firing accelerations and the harsh firing environment. Reliability is also of much concern since the rounds need to have a shelf life of up to 20 years and could generally be stored at temperatures in the range of −65 to 165 degrees F.
In addition, for years, munitions developers have struggled with the placement of components, such as sensors, processors, actuation devices, communications elements and the like within a munitions housing and providing physical interconnections between such components. This task has become even more difficult with the increasing requirement of making gun-fired munitions and mortars smarter and capable of being guided to their stationary and moving targets. It is, therefore, extremely important for all guidance and control actuation devices, their electronics and power sources not to significantly add to the existing problems of integration into the limited projectile volume.